Using a variety of molecular biology and biochemical virology techniques, we have examined the structure of the acquired immunodeficiency syndrome (AIDS) retrovirus (RV) and characterized viral gene products synthesized in infected cells. Druing the past year the nucleotide sequences of the envelope (env) genes of an African and North American AIDS viral isolate have been determined. When their deduced amino acid sequences were aligned with the envelopes of the LAV and ARV isolates, conserved and divergent regions were readily identified. Hypervariabile stretches of 28 to 74 amino acids, exhibiting 20 to 30% amino acid identity at each position and characterized by reciprocal insertions and deletions, were confined to the gp120 external env protein. The env gene diversity, observed among different AIDS RV isolates, suggests the involvement of the immune system at some point during viral infection and does not augur well for rapid development of an effective vaccine. We have constructed an infectious molecular clone of acquired immunodeficiency syndrome-associated retrovirus. Upon transfection, this clone directed the production of infectious virus particles in a wide variety of cells in addition to human T4 cells. Infectious progeny virions were synthesized in mouse, mink, monkey, and several human non-T cell lines indicating the absence of any intracellular obstacle to viral RNA or protein production or assembly. Thirteen adherent human non-lymphocyte cell lines also were tested for their susceptibility to infection by the AIDS retrovirus. Productive infection could be demonstrated in 3 or 5 colorectal carcinoma cell lines examined; the other 8 human non-lymphocyte cells lines were uninfectible. A susceptible colon carcinoma cell line (HT29) as well as normal colonic mucosa were shown to contain a 3.0 kb species of polyadenylated CD4 RNA whereas unifectible colon carcinoma and rhabdomyosarcoma cell lines synthesized no detectable T4 RNA. A persistently infected colon carcinoma cell line was established that continued to produce progeny AIDS virus for more than 10 weeks post-infection.